Analog front-end circuitry and brain-computer interface integrating neural stimulation and acquisition

Abstract

This application relates to the field of bioelectric signal processing technology, and discloses an integrated analog front-end circuit and brain-computer interface system for neural stimulation and acquisition. The analog front-end circuit includes multiple electrodes, a stimulation module, and a signal acquisition module. The stimulation module and signal acquisition module are respectively connected to the multiple electrodes. Any two electrodes are selected as stimulation electrodes, and the remaining electrodes are acquisition electrodes. The stimulation module is configured to control two stimulation electrodes to be alternately grounded during the stimulation cycle, and to cause the ungrounded stimulation electrode to output a stimulation signal. The signal acquisition module includes multiple signal channels corresponding one-to-one with the electrodes. The signal acquisition module is configured to turn off the signal channel corresponding to the stimulation electrode and synchronously switch the on / off state of the signal channel corresponding to the acquisition electrode during the stimulation cycle, so as to acquire physiological signals in response to the stimulation signal during non-stimulation cycles. This application can effectively suppress stimulation artifacts and achieve high-fidelity physiological signal acquisition.

Description

Technical Field

[0001] This application relates to the field of bioelectric signal processing technology, and in particular to an analog front-end circuit and brain-computer interface system that integrates neural stimulation and acquisition. Background Technology

[0002] Invasive neural stimulation and acquisition systems are widely used in applications such as neural function modulation, brain-computer interfaces, and treatment of neurological diseases. They can both apply electrical stimulation to neural tissue and acquire weak neural electrical signals after stimulation, providing data support for closed-loop neural modulation.

[0003] Because electrodes directly contact nerve tissue in invasive scenarios, the stimulation signal is a high-voltage, high-current pulse, while the acquisition signal is a weak signal at the microvolt level. The two are very prone to mutual interference, and related technologies have difficulty effectively suppressing the signal interference between the stimulation signal and the acquisition signal, resulting in the system being unable to achieve high-precision nerve signal acquisition while stimulating nerve tissue. Summary of the Invention

[0004] This application provides an analog front-end circuit and brain-computer interface system that integrates neural stimulation and acquisition. It solves the technical problem that neural stimulation and acquisition systems are unable to effectively suppress signal interference between stimulation signals and acquisition signals, which leads to the inability of the system to achieve high-precision neural signal acquisition. It achieves the technical effect of effectively suppressing stimulation artifacts and realizing high-fidelity physiological signal acquisition.

[0005] To achieve the above objectives, the main technical solutions adopted in this application include: In a first aspect, this application provides an analog front-end circuit that integrates neural stimulation and acquisition. The analog front-end circuit includes multiple electrodes, a stimulation module, and a signal acquisition module. The stimulation module and the signal acquisition module are respectively connected to the multiple electrodes. Any two of the electrodes are selected as stimulation electrodes, and the remaining electrodes are acquisition electrodes. The stimulation module includes a constant current source unit configured to generate a stimulation signal. The stimulation module is configured to control the two stimulation electrodes to be alternately grounded during the stimulation cycle, and to make the ungrounded stimulation electrode output a stimulation signal. The grounding is connected to the negative terminal of the constant current source unit. The signal acquisition module includes multiple signal channels corresponding to each of the electrodes. The signal acquisition module is configured to turn off the signal channel corresponding to the stimulation electrode and synchronously switch the on / off state of the signal channel corresponding to the acquisition electrode during the stimulation cycle, so as to acquire physiological signals in response to the stimulation signal during non-stimulation cycles.

[0006] The analog front-end circuit proposed in this application utilizes the alternating grounding of two stimulation electrodes during the stimulation cycle to achieve commutated output of the stimulation signal. This not only avoids charge accumulation on the stimulation electrodes, ensuring the safety of the stimulation process, but also effectively suppresses the common-mode voltage of the stimulation signal relative to the circuit ground, thereby reducing the artifact energy of the stimulation signal coupled to the acquisition channel through parasitic paths. Simultaneously, the signal acquisition module shuts off the signal channel corresponding to the stimulation electrode and synchronously switches the on / off state of the signal channel corresponding to the acquisition electrode during the stimulation cycle. This ensures that the acquisition path is disconnected during stimulation, preventing stimulation artifacts from entering the acquisition results, while the acquisition path is restored during non-stimulation periods, thus allowing normal acquisition of physiological signals. This effectively avoids signal distortion and artifact interference caused by the coupling of the stimulation signal to the acquisition path, thereby ensuring high fidelity of neural signal acquisition under conditions of synchronous stimulation and acquisition.

[0007] It should be noted that in this application, the term "grounding" does not refer to the connection to earth, the metal casing of equipment, or the common reference ground in electrical engineering or general electronics. In general technical terms, "grounding" typically refers to a low-impedance connection between a node in a circuit and the earth's potential or the zero-potential reference plane of the entire system (such as a chassis or common ground wire) to provide safety protection, electromagnetic compatibility reference, or a zero-potential reference for signals. However, this application relates to invasive neural stimulation and acquisition, in which electrodes are inserted into biological tissue, while the stimulation module and signal acquisition module are located externally and connected to the internal electrodes via wires. The stimulation current loop consists only of the positive terminal of the constant current source unit, the internal electrode selected as the stimulation electrode, the biological tissue, and the negative terminal of the constant current source unit, without passing through, and not permitted to be connected to, actual earth. Therefore, the term "grounding" in this application specifically refers to connection to the negative terminal (i.e., the current return terminal) of the constant current source unit in the stimulation module.

[0008] Specifically, during the stimulation cycle, the two selected stimulation electrodes are alternately switched via an internal switch. The electrode not outputting a stimulation signal is not left floating or connected to an absolute zero potential, but is connected to the negative terminal of the constant current source unit, while the other stimulation electrode is connected to the positive terminal of the constant current source unit to output a stimulation signal. In this way, the stimulation current is injected into the biological tissue from the positive electrode, flows through the target nerve region, and then returns to the constant current source unit from the negative electrode, forming a complete bipolar constant current stimulation circuit. Therefore, the actual meaning of "alternating grounding of stimulation electrodes" is to alternately connect the negative terminal of the constant current source unit, allowing the two stimulation electrodes to act as current return terminals in a time-sharing manner, thereby achieving directional charge flow, alternating reverse stimulation, or charge-balanced stimulation. Due to the requirements of precise control of the stimulation current and biosafety, connecting the electrode circuit to the ground or the equipment's common ground would cause the stimulation current to fail to form the prescribed circuit, resulting in stimulation energy leakage or uncontrollability, damaging the stimulation effect and potentially causing safety issues. Therefore, the term "grounding" as used in this application should be understood in the specific sense defined here, that is, specifically referring to the connection to the negative terminal (current return terminal) of the constant current source unit in the external stimulation module. The so-called "alternating grounding of stimulation electrodes" actually means that the two stimulation electrodes are alternately connected to the negative terminal of the constant current source unit during the stimulation cycle, so as to act as current return electrodes in a time-sharing manner, and do not mean that they are connected to the earth or the system common ground.

[0009] Optionally, the stimulation module further includes: The H-bridge switching unit includes a first bridge arm and a second bridge arm. The middle node of the first bridge arm is connected to one of the stimulation electrodes, and the middle node of the second bridge arm is connected to the other stimulation electrode. The first ends of the first bridge arm and the second bridge arm are respectively adapted to receive the stimulation signal, and the second ends of the first bridge arm and the second bridge arm are respectively grounded. The first bridge arm and the second bridge arm respectively include a high-side switch and a low-side switch. The H-bridge switching unit is configured to switch the on / off state of the high-side switch and the low-side switch to alternately change the output circuit of the constant current source unit, so that the two stimulation electrodes are alternately grounded during the stimulation cycle. A control unit is configured to control the constant current source to generate the stimulation signal and to control the on / off states of the high-side switch and the low-side switch.

[0010] By controlling the switching of the bridge arm structure, bidirectional symmetrical stimulation is achieved, avoiding charge accumulation caused by unidirectional current. At the same time, due to the alternating grounding connection method, the common-mode voltage of the stimulation electrode to ground is effectively limited, thereby significantly reducing the amplitude of stimulation artifacts and facilitating the acquisition of high-fidelity neural signals.

[0011] Optionally, the stimulation module further includes a dummy load unit, which is configured to connect to the output circuit of the constant current source unit during the commutation of the stimulation signal to suppress commutation glitches in the stimulation signal.

[0012] By setting a dummy load unit in the stimulation module and connecting it to the current loop of the constant current source unit during the commutation of the stimulation signal, the constant current source is kept under load during the switching process, avoiding the output voltage runaway spike caused by momentary open circuit. This effectively suppresses voltage glitches generated during the commutation process, improves the waveform quality of the stimulation pulse and the safety of the stimulation process.

[0013] Optionally, the stimulation module further includes an impedance testing unit and a mode switching unit; The mode switching unit is configured to control the H-bridge switching unit to connect to one of the constant current source unit and the impedance testing unit; The impedance testing unit is configured to measure the impedance between the stimulation electrodes when the H-bridge switch unit is connected to the impedance testing unit, so as to detect whether the stimulation electrodes have abnormal contact based on the measurement results.

[0014] The mode switching unit controls the H-bridge switch unit to select between the constant current source unit and the impedance testing unit. When switched to the impedance testing unit, by applying a test signal to the stimulation electrode and measuring the bioimpedance, contact impedance information between the electrode and the tissue can be obtained without adding additional electrodes and wiring. This facilitates the assessment of electrode contact status before or during stimulation, providing a basis for judging stimulation safety and reducing the risk of stimulation failure or tissue damage due to poor contact.

[0015] Optionally, each of the signal channels includes: A pre-amplifier analog switch unit is configured to be turned off when the signal channel corresponds to the stimulation electrode and turned on when the signal channel corresponds to the acquisition electrode, so as to acquire the physiological signal acquired by the acquisition electrode. An amplifier unit is configured to amplify the acquired physiological signal and output the amplified physiological signal. The post-stage analog switching unit is configured to switch on and off synchronously with the stimulation cycle, such that the signal channel corresponding to the acquisition electrode is turned off during the stimulation cycle and turned on during the non-stimulation cycle, so as to transmit the amplified physiological signal to the post-stage circuit during the non-stimulation cycle.

[0016] By placing the analog switch after the instrumentation amplifier, the charge injection artifacts generated by its switching action are not further amplified by the instrumentation amplifier, thus significantly reducing their impact on the physiological signal to be transmitted. In this way, while effectively suppressing stimulation artifacts, the signal distortion caused by excessive amplification of pre-amplifier switch artifacts in traditional schemes is avoided, further improving the signal-to-noise ratio and fidelity of the output signal.

[0017] Optionally, each of the signal channels further includes a voltage follower unit and a low-pass filter unit, wherein the voltage follower unit is connected between the front-end analog switch unit and the low-pass filter unit, and the low-pass filter unit is connected between the voltage follower unit and the amplifier unit.

[0018] By leveraging the high input impedance and low bias current characteristics of voltage followers, high input impedance can be provided without the need for additional bias resistors in the amplifier unit. This overcomes the common-mode rejection ratio (CMRR) degradation caused by the large and significant differences in contact impedance of invasive electrodes, effectively suppressing power frequency interference and stimulating common-mode interference. Simultaneously, a low-pass filter unit is used to filter out high-frequency radio frequency interference. This approach ensures high CMRR performance in the analog front-end circuit while avoiding the input impedance limitation imposed by bias resistors in traditional solutions, thus providing a high-fidelity input signal for subsequent instrumentation amplifiers.

[0019] Optionally, each of the signal channels further includes an adjustable high-pass filter unit connected between the amplifier unit and the subsequent analog switching unit.

[0020] This application enables the signal baseline to recover and stabilize quickly by setting the time constant of the adjustable high-pass filter unit, thereby significantly shortening the signal stabilization time after stimulation. This facilitates rapid and reliable continuous acquisition and improves the acquisition efficiency of physiological signals.

[0021] Optionally, the analog front-end circuit further includes an isolation module configured to electrically isolate the stimulation module and the signal acquisition module.

[0022] This application uses an isolation module to block the unexpected path of the stimulation current returning through the neutral electrode and reduces the ground interference between the stimulation circuit and the acquisition circuit, further reducing the coupling energy of the stimulation signal to the acquisition channel, which is beneficial to achieving high-precision physiological signal acquisition.

[0023] Optionally, the isolation module includes an isolation communication module configured to transmit the clock signal of the stimulation cycle to the signal acquisition module in isolation, so that the signal acquisition module switches the on / off state of the signal channel corresponding to the acquisition electrode in sync with the stimulation cycle based on the clock signal.

[0024] The clock signal of the stimulation cycle is transmitted to the signal acquisition module in an electrically isolated manner through an isolated communication module, enabling the signal acquisition module to accurately synchronize with the on / off state of the stimulation cycle switching signal channel based on this clock signal. Thus, while ensuring electrical isolation between the stimulation module and the signal acquisition module and blocking interference paths, precise timing coordination between the two is achieved, avoiding artifact leakage caused by timing deviations, and further improving the reliability of stimulation synchronization and the quality of the acquired signal.

[0025] Secondly, embodiments of this application provide a brain-computer interface system, the brain-computer interface system comprising: System host; And an integrated analog front-end circuit for neural stimulation and acquisition, as described above, which is connected to the system host. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 A schematic diagram of an analog front-end circuit integrating neural stimulation and acquisition provided in an embodiment of this application; Figure 2 A schematic diagram of the circuit structure of a stimulation module provided in an embodiment of this application; Figure 3 This is a schematic diagram of the switching timing of the stimulation module in an embodiment of this application; Figure 4 A schematic diagram of the circuit structure of a stimulation module provided in another embodiment of this application; Figure 5 A schematic diagram of the circuit structure of the signal channel provided in an embodiment of this application; Figure 6(a) is a schematic diagram of the working principle of the piercing synchronous electrode in the related technology; Figure 6(b) is a schematic diagram of the working principle of the isolation module provided in the embodiment of this application; Figure 7 This is a schematic diagram of the brain-computer interface system provided in an embodiment of this application. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms "comprising" and "having," and any variations thereof, in the description, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the description, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or hierarchy.

[0030] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0031] Invasive neural stimulation and acquisition systems need to be able to apply electrical stimulation to nerve tissue and acquire weak neural electrical signals after stimulation in real time, such as action potentials, field potentials (LFP), and ECAP signals, to provide data support for closed-loop neural modulation.

[0032] In some related technologies, dedicated integrated chips are used to achieve neural stimulation and physiological signal acquisition. These chips are usually single-function designs, either for multi-channel acquisition or multi-channel stimulation, and are not specifically designed for synchronous and coordinated stimulation and acquisition. If the two types of chips are simply combined, the acquisition chip takes a weak EEG signal at the microvolt level as input and outputs a digital signal quantized by an ADC. Its signal chain is internally closed, making it impossible to flexibly insert artifact suppression or timing shielding circuits at the analog front end, thus limiting the means of handling stimulation artifacts. Even if a few integrated chips that combine stimulation and acquisition exist, they are merely simple encapsulations of the two types of circuits. They not only suffer from the same defects of difficulty in handling artifacts and non-scalable signal chains, but also, in multi-channel synchronous stimulation applications, there are generally multiple signal electrodes, one reference electrode, and one neutral electrode. The neutral electrode is used to connect to the human body for isoelectricity or to drive the right leg. Some stimulation current may form an unexpected return path from the neutral electrode, causing bipolar stimulation charge imbalance, thereby prolonging artifact recovery time and potentially causing tissue damage.

[0033] In other related technologies, stimulation acquisition synchronization circuits built with discrete components offer a degree of architectural flexibility. However, regardless of whether the signal acquisition circuit is built with integrated chips or discrete components, its basic structure typically includes units such as low-pass filtering for radio frequency interference, pre-amplification, high-pass filtering, post-amplification, and analog-to-digital sampling. Although the circuit employs an instrumentation amplifier with a high common-mode rejection ratio (CMRR), which performs excellently in ideal laboratory environments, in clinical settings, the high contact impedance of the human electrodes and significant impedance differences between electrodes lead to an imbalance in the signal impedance at the two input terminals of the instrumentation amplifier. This results in a significant decrease in the system's CMRR, making it difficult to effectively resist power frequency common-mode interference or common-mode interference caused by stimulation. Furthermore, some related technologies control an analog switch to disconnect the signal acquisition path during stimulation to shield stimulation energy. However, while this method suppresses stimulation artifacts, interference from the analog switch's operation remains, resulting in an overall less than ideal suppression effect.

[0034] Therefore, there is an urgent need for a high-precision and high-reliability neural stimulation and acquisition coordination scheme.

[0035] This application provides an integrated analog front-end circuit 10 for neural stimulation and acquisition. This analog front-end circuit 10 can be used in devices such as puncture-synchronous electroencephalography (EEG) machines, deep brain stimulation (DBS) systems, and brain-computer interfaces. Figure 1 As shown, the analog front-end circuit 10 includes multiple electrodes, a stimulation module 11, and a signal acquisition module 12. The stimulation module 11 and the signal acquisition module 12 are respectively connected to the multiple electrodes. Any two of the electrodes are selected as stimulation electrodes, and the remaining electrodes are acquisition electrodes.

[0036] The stimulation module 11 includes a constant current source unit 111, which is configured to generate a stimulation signal. The stimulation module 11 is configured to control two stimulation electrodes to be alternately grounded during the stimulation cycle, and to make the ungrounded stimulation electrode output a stimulation signal.

[0037] It should be noted that in this application, the term "grounding" does not refer to connection to the earth, the metal casing of an equipment, or the common reference ground of a system as understood in electrical engineering or general electronics. Instead, it refers to connection to the negative terminal of the constant current source unit 111. In general technical terms, "grounding" typically refers to a low-impedance connection between a node in a circuit and the earth's potential or the zero-potential reference plane of the entire system (such as a chassis or common ground wire) to provide safety protection, electromagnetic compatibility reference, or a zero-potential reference for signals. However, this application relates to invasive neural stimulation and acquisition, in which electrodes are inserted into biological tissue, while the stimulation module and signal acquisition module are located externally and connected to the internal electrodes via wires. The stimulation current loop consists only of the positive terminal of the constant current source unit 111, the internal electrode selected as the stimulation electrode, the biological tissue, and the negative terminal of the constant current source unit 111, without passing through, and not permitted to be connected to, the actual earth. Therefore, the term "grounding" in this application specifically refers to connection to the negative terminal (i.e., the current return terminal) of the constant current source unit 111 in the stimulation module.

[0038] Specifically, during the stimulation cycle, the two selected stimulation electrodes are alternately switched via an internal switch. The electrode not outputting a stimulation signal is not suspended or connected to an absolute zero potential, but is connected to the negative terminal of the constant current source unit 111, while the other stimulation electrode is connected to the positive terminal of the constant current source unit 111 to output a stimulation signal. In this way, the stimulation current is injected into the biological tissue from the positive electrode, flows through the target nerve region, and then flows back to the constant current source unit 111 from the negative electrode, forming a complete bipolar constant current stimulation circuit. Therefore, the actual meaning of "alternating grounding of stimulation electrodes" is alternating connection of the negative terminal of the constant current source unit 111, allowing the two stimulation electrodes to act as current return terminals in a time-sharing manner, thereby achieving directional charge flow, alternating reverse stimulation, or charge-balanced stimulation. Due to the requirements of precise control of the stimulation current and biosafety, connecting the electrode circuit to the ground or the equipment's common ground would result in the stimulation current failing to form a proper circuit, stimulation energy leakage or uncontrollability, damaging the stimulation effect and potentially causing safety issues. Therefore, the term "grounding" as used in this application should be understood in the specific sense defined here, that is, it specifically refers to the connection to the negative terminal (current return terminal) of the constant current source unit 111 in the external stimulation module. The so-called "alternating grounding of stimulation electrodes" actually means that the two stimulation electrodes alternately connect to the negative terminal of the constant current source unit 111 during the stimulation cycle to act as current return electrodes in a time-sharing manner, and does not mean that they are connected to the earth or the system common ground.

[0039] Specifically, the stimulation module 11 selects any two electrodes from the multiple electrodes specified by the user or system command as the stimulation electrodes for this stimulation. It should be noted that in this embodiment, the stimulation signal is a stimulation current, and the stimulation period refers to the time interval required to output at least one complete stimulation signal. This stimulation signal typically includes two phases, corresponding to the output phases of a positive pulse and a negative pulse, respectively. In one phase within a stimulation period, the stimulation module 11 first connects the first stimulation electrode to ground, and the second stimulation electrode is connected to the output terminal of the stimulation signal. At this time, the second stimulation electrode outputs a stimulation signal to the nerve tissue. Subsequently, in the next phase of the stimulation period, the stimulation module 11 swaps the grounding and output terminals, grounding the second stimulation electrode and allowing the first stimulation electrode to output a stimulation signal. This process is repeated, with the two stimulation electrodes alternately at ground potential within the stimulation period, while the other electrode undertakes the signal output task, thus forming a bidirectional pulse output with alternating grounding.

[0040] Understandably, bipolar stimulation must be used in neuromuscular electrical stimulation applications. Firstly, for safety reasons, an imbalance in the stimulation charge can lead to net charge accumulation at the electrode-tissue interface, potentially causing electrochemical burns and irreversible tissue damage over time. Secondly, for effectiveness, capacitive coupling typically exists in the stimulation output path, and an equivalent capacitance is formed at the electrode-tissue interface. If unipolar stimulation is used, these capacitances will gradually become saturated, preventing subsequent stimulation current from effectively reaching the target tissue and thus losing its stimulation effect. Therefore, this embodiment employs bipolar stimulation to ensure the safety of the stimulation process. Furthermore, in different phases of the stimulation cycle, the two stimulation electrodes are alternately shorted to the circuit's ground potential. This ensures that at any given moment, one stimulation electrode has a voltage at ground potential, while the voltage of the other electrode is determined solely by the product of the stimulation current and tissue resistance, typically a few volts. This limits the common-mode voltage of the stimulation circuit to ground to an extremely low level, effectively reducing artifact energy from the stimulation signal coupling to the acquisition channel through parasitic capacitance or human tissue.

[0041] The signal acquisition module 12 includes multiple signal channels corresponding to each electrode. The signal acquisition module 12 is configured to turn off the signal channel corresponding to the stimulation electrode and synchronously switch the on / off state of the signal channel corresponding to the acquisition electrode during the stimulation cycle, so as to acquire physiological signals in response to the stimulation signal during the non-stimulation cycle.

[0042] Specifically, each signal channel is independently connected to an electrode. For signal channels corresponding to those selected as stimulation electrodes, the signal acquisition module 12 shuts them off, keeping the acquisition path of that channel disconnected to prevent high-voltage stimulation signals from entering the acquisition link and damaging subsequent circuits or generating additional interference. For signal channels corresponding to acquisition electrodes not selected as stimulation electrodes, the signal acquisition module 12 switches them on and off according to the stimulation cycle sequence. During the stimulation cycle, i.e., during the output of stimulation signals, these signal channels are synchronously disconnected, ensuring that any stimulation artifacts or external interference such as switching actions during this period will not affect the acquisition results of physiological signals. During non-stimulation cycles, i.e., when there is no stimulation signal output, these signal channels are reconnected, allowing the physiological signals acquired by the acquisition electrodes to be transmitted normally to the subsequent processing circuits. This ensures that the physiological signal acquisition path is only effective during non-stimulation periods, thus isolating the interference energy generated during stimulation from the acquisition results, while not affecting the normal acquisition of stimulation-induced physiological signals.

[0043] The analog front-end circuit 10 provided in this embodiment utilizes the alternating grounding of two stimulation electrodes during the stimulation cycle to achieve commutated output of the stimulation signal. This not only avoids charge accumulation on the stimulation electrodes, ensuring the safety of the stimulation process, but also effectively suppresses the common-mode voltage of the stimulation signal relative to the circuit ground, thereby reducing the artifact energy of the stimulation signal coupled to the acquisition channel through parasitic paths. Simultaneously, the signal acquisition module 12 shuts off the signal channel corresponding to the stimulation electrode and synchronously switches the on / off state of the signal channel corresponding to the acquisition electrode during the stimulation cycle. This ensures that the acquisition path is disconnected during stimulation, preventing stimulation artifacts from entering the acquisition results, while the acquisition path is restored during non-stimulation periods, thus allowing normal acquisition of physiological signals. This effectively avoids signal distortion and artifact interference caused by the coupling of the stimulation signal to the acquisition path, thereby ensuring high fidelity of neural signal acquisition under conditions of synchronous stimulation and acquisition.

[0044] Figure 2 The circuit structure of the stimulation module 11 described above is shown in one embodiment of this application, as follows: Figure 2As shown, the stimulation module 11 also includes an H-bridge switching unit 112 and a control unit 113 (Micro Control Unit, MCU). The constant current source unit 111 is configured to generate a stimulation signal. The H-bridge switching unit 112 includes a first arm and a second arm. The middle node of the first arm is connected to one stimulation electrode, and the middle node of the second arm is connected to another stimulation electrode. The first ends of the first and second arms are adapted to receive stimulation signals, and the second ends of the first and second arms are grounded. The first and second arms each include a high-side switch and a low-side switch. The H-bridge switching unit 112 is configured to switch the on / off states of the high-side switch and the low-side switch to alternately change the output circuit of the constant current source unit 111, so that the two stimulation electrodes are alternately grounded during the stimulation cycle. The control unit 113 is configured to control the constant current source to generate the stimulation signal and to control the on / off states of the high-side switch and the low-side switch.

[0045] Specifically, in this embodiment of the application, the constant current source unit 111 adopts a current output type digital-to-analog converter (DAC) constant current source, which is used to generate a constant current stimulation signal with a set amplitude under the control command issued by the control unit 113. The control unit 113 configures the stimulation current value of the constant current source unit 111 through the SPI interface 1.

[0046] The H-bridge switching unit 112 consists of a first bridge arm and a second bridge arm. The first bridge arm includes a high-side switch S1 and a low-side switch S2 connected in series, and the second bridge arm includes a high-side switch S3 and a low-side switch S4 connected in series. The middle node of the first bridge arm, which is the connection node between the high-side switch S1 and the low-side switch S2, is connected to electrode 1, which serves as the stimulation electrode. The middle node of the second bridge arm, which is the connection node between the high-side switch S3 and the low-side switch S4, is connected to electrode 2, which serves as the stimulation electrode. The first ends of the first and second bridge arms, namely the ends of the high-side switches S1 and S3 except for the middle node, are connected to one output terminal of the constant current source unit 111. The second ends of the first and second bridge arms, namely the ends of the low-side switches S2 and S4 except for the middle node, are connected to the other output terminal of the constant current source unit 111 and grounded.

[0047] The control unit 113 controls the on / off state of each switch via the I / O interface. When positive stimulation is required, the control unit 113 turns on the high-side switch S1 and the low-side switch S4. Current flows from the constant current source output terminal through the high-side switch S1 to electrode 1, passes through the human tissue to reach electrode 2, and then returns to ground through the low-side switch S4. At this time, electrode 2 is grounded, and electrode 1 outputs a stimulation signal with a positive pulse current stimulation waveform. When reverse stimulation is required, the control unit 113 turns on the high-side switch S3 and the low-side switch S2. Current flows from the constant current source output terminal through the high-side switch S3 to electrode 2, passes through the human tissue to reach electrode 1, and then returns to ground through the low-side switch S2. At this time, electrode 1 is grounded, and electrode 2 outputs a stimulation signal with a positive pulse current stimulation waveform. This forms bidirectional symmetrical stimulation, avoiding charge accumulation that could cause electrode polarization and preventing damage to the stimulated tissue.

[0048] Because the output circuit of the constant current source unit 111 in this embodiment is set at the low end, i.e., the second terminal of the H-bridge switching unit 112 is grounded, taking a power supply voltage of 30V, a stimulation current of 1mA, and a load resistance of 1kΩ as an example, the voltage drop across the load is 1V. At this time, the voltages across the load to ground are 0V and 1V, respectively, and the differential voltage is 1V. In the conventional scheme, the output circuit of the constant current source is set at the power supply end. Under the same conditions, the voltages across the load to ground are 30V and 29V, respectively. Although the differential voltage is 1V, its common-mode voltage relative to the reference ground of the acquisition circuit is as high as 29V. It can be seen that by switching the bridge arm structure described above, the current loop of the constant current source unit 111 is alternately changed, thereby realizing the alternating grounding of the two stimulation electrodes during the stimulation cycle. At the same time, the common-mode voltage of the stimulation signal relative to the acquisition reference ground of the acquisition module is reduced from tens of volts to a low voltage level determined only by the stimulation current and the load resistance, thereby significantly weakening the coupling energy of the stimulation artifact from the source.

[0049] The embodiments of this application achieve bidirectional symmetrical stimulation by switching the bridge arm structure, avoiding charge accumulation caused by unidirectional current. At the same time, due to the alternating grounding connection method, the common-mode voltage of the stimulation electrode to ground is effectively limited, thereby significantly reducing the amplitude of stimulation artifacts and facilitating the acquisition of high-fidelity neural signals.

[0050] like Figure 2 As shown, the stimulation module 11 also includes a dummy load unit 114, which is configured to connect to the output circuit of the constant current source unit 111 during the commutation of the stimulation signal in order to suppress commutation glitches of the stimulation signal.

[0051] When the stimulation signal commutates, there is a moment when both switches S1 and S3 are open. At this time, the constant current source unit 111 has no load, and its output voltage is its maximum output voltage Vmax. When the negative phase stimulation signal is output, switches S2 and S3 close, and the constant current source unit 111 is connected to the electrode load. At this time, the voltage across the electrode load is Vmax. Since the constant current source unit 111 needs time to adjust and recover, a voltage spike will be generated across the electrode load.

[0052] Specifically, the dummy load unit 114 includes a dummy load resistor R1 and a control switch S5. One end of the dummy load resistor R1 is connected to an output terminal of the constant current source unit 111 and an input terminal of the high-side switch in the H-bridge switch unit 112 via the control switch S5. The other end of the dummy load resistor R1 is connected to an output terminal of the constant current source unit 111 and grounded. During the commutation of the stimulation signal, the control unit 113 closes the control switch S5, connecting the dummy load resistor R1 to the output circuit of the constant current source unit 111. This ensures that the constant current source always has a load circuit during the commutation process, avoiding output voltage runaway and spikes caused by momentary open circuits.

[0053] Figure 3 A schematic diagram of the switching timing of the stimulation module 11 is shown, as follows: Figure 3As shown, in some embodiments of this application, a stimulation cycle sequentially includes a positive pulse output phase, a pulse interval phase, a negative pulse output phase, and an active charge balance phase. During non-stimulation cycles, the stimulation circuit is idle, and the constant current source output current is zero, meaning no stimulation signal is output. The control unit 113 closes switch S5, and the dummy load resistor R1 serves as the sole load of the constant current source. Upon entering the positive pulse output phase, the control unit 113 first configures the constant current source unit 111 to output a set positive current as the stimulation signal, then controls switches S1 and S4 to close. After a delay t, switch S5 is opened, at which point the dummy load is removed. Therefore, the current path corresponding to the stimulation signal is constant current source unit 111 through switch S1, electrode 1, human tissue, electrode 2, switch S4 to ground, and the stimulation current is normally applied to the tissue. Before the positive pulse ends, the control unit 113 controls switch S5 to close a certain time t in advance, reconnecting the dummy load, and then opens switches S1 and S4 to ensure that the constant current source unit 111 always carries a load during the switching process. During the subsequent pulse interval phase, corresponding to the commutation period of the stimulation signal, switches S1 to S4 of the H-bridge are all open, with only switch S5 remaining closed. The load of the constant current source unit 111 is the dummy load resistor R1. The operation of the negative pulse output phase is similar to that of the positive pulse output phase. The control unit 113 first configures the constant current source unit 111 to output a set negative current as the stimulation signal, then controls switches S2 and S3 to close, and after a delay t, switches S5 is opened. At this time, the current path corresponding to the stimulation signal is constant current source unit 111 through switch S3, electrode 2, human tissue, electrode 1, switch S2 to ground, and the stimulation current is normally applied to the tissue. Before the end of the negative pulse, switch S5 is closed a certain time in advance, and then switches S2 and S3 are opened. Finally, after each bidirectional stimulation pulse ends, the active charge balance phase begins. At this time, the control unit 113 controls switches S2 and S4 to close, shorting the two stimulation electrodes to ground to release residual charge. This ensures that the net charge between the electrode and the nerve tissue is zero during stimulation, avoiding charge accumulation that could cause electrode polarization and tissue damage, while also shortening the baseline recovery time after stimulation.

[0054] In one example of an embodiment of this application, the control unit 113 can be a microcontroller of model STM32F103VBI6, the constant current source unit 111 can be a current output DAC of model AD5422, and the H-bridge switch unit 112 can be a switch chip of model TMUX7208. The aforementioned switch S5 can be an analog switch of model ADG5412. Since its turn-on and turn-off time is 260ns, the aforementioned time t can be set to 300~500ns, and the impact on the stimulation pulse width accuracy of 10µs-500µs can be ignored.

[0055] This embodiment of the application sets up a dummy load unit 114 in the stimulation module 11 and connects it to the current loop of the constant current source unit 111 during the commutation of the stimulation signal. This ensures that the constant current source is always under load during the switching process, avoiding output voltage runaway spikes caused by momentary open circuit. This effectively suppresses voltage glitches generated during the commutation process, improves the waveform quality of the stimulation pulse and the safety of the stimulation process.

[0056] Figure 4 The circuit structure of the stimulation module 11 described above is shown in another embodiment of this application, as follows: Figure 4 As shown, the stimulation module 11 also includes an impedance testing unit 115 and a mode switching unit 116. The mode switching unit 116 is configured to control the H-bridge switch unit 112 to connect to one of the constant current source unit 111 and the impedance testing unit 115. The impedance testing unit 115 is configured to measure the impedance between the stimulation electrodes when the H-bridge switch unit 112 is connected to the impedance testing unit 115, in order to detect whether there is abnormal contact between the stimulation electrodes based on the measurement results.

[0057] Specifically, the mode switching unit 116 consists of a set of analog switches S6 to S9. Switches S6 and S7 are connected in series between the constant current source unit 111 and the H-bridge switch unit 112, and switches S8 and S9 are connected in series between the impedance testing unit 115 and the H-bridge switch unit 112. When stimulation is required, the control unit 113 closes switches S6 and S7 and opens switches S8 and S9. At this time, the H-bridge switch unit 112 is connected to the constant current source unit 111, and the stimulation module 11 operates in stimulation mode. When impedance testing is required, the control unit 113 closes switches S8 and S9 and opens switches S6 and S7. At this time, the H-bridge switch unit 112 is connected to the impedance testing unit 115, and the stimulation module 11 switches to impedance testing mode.

[0058] In one example of this application embodiment, the impedance testing unit 115 can employ an integrated chip of model AD5941, and the switching switches S6 to S9 in the mode switching unit 116 can employ analog switches of model ADG5413. The integrated chip can generate test signals, which are applied to any two selected stimulation electrodes via the H-bridge switching unit 112. After the test signal flows through the contact interface between the electrode and the tissue, the impedance testing unit 115 calculates the bioimpedance value based on the measured voltage-to-current ratio. Since the contact impedance between human tissue and the electrode can reflect whether the electrode contacts are short-circuited, open-circuited, or have poor contact, the control unit 113 can determine whether the electrode is suitable for subsequent stimulation operations based on this impedance value. In practical use, for example, after electrode implantation or before each stimulation begins, the system can first switch to the impedance testing mode to quickly detect the contact state between the electrode and the tissue. If an impedance abnormality is detected, an alarm is issued or stimulation is prohibited. Through the setting of the mode switching unit 116, this embodiment achieves the reuse of stimulation and impedance testing functions without adding extra electrodes and complex wiring, providing assurance for the safety and effectiveness of stimulation.

[0059] In this embodiment, the mode switching unit 116 controls the H-bridge switching unit 112 to select between the constant current source unit 111 and the impedance testing unit 115. When switched to the impedance testing unit 115, by applying a test signal to the stimulation electrode and measuring the bioimpedance, contact impedance information between the electrode and the tissue can be obtained without adding additional electrodes and wiring. This facilitates the assessment of electrode contact status before stimulation or during stimulation intervals, providing a basis for judging stimulation safety and reducing the risk of stimulation failure or tissue damage due to poor contact.

[0060] like Figure 5 As shown, each signal channel includes a pre-stage analog switch unit 121, an amplifier unit 122, and a post-stage analog switch unit 123. The pre-stage analog switch unit 121 is configured to be off when the signal channel corresponds to a stimulation electrode and on when the signal channel corresponds to a acquisition electrode, to acquire the physiological signal collected by the acquisition electrode. The amplifier unit 122 is configured to amplify the acquired physiological signal and output the amplified physiological signal. The post-stage analog switch unit 123 is configured to switch on and off synchronously with the stimulation cycle, so that the signal channel corresponding to the acquisition electrode is off during the stimulation cycle and on during the non-stimulation cycle, so as to transmit the amplified physiological signal to the post-stage circuit during the non-stimulation cycle.

[0061] Specifically, in some embodiments of this application, each signal channel further includes a Field Programmable Gate Array (FPGA) unit, and the signal channel is controlled by the FPGA unit as the main controller to control the aforementioned front-end analog switch unit 121 and rear-end analog switch unit 123.

[0062] Each signal channel is front-end equipped with a pre-amplifier analog switch unit 121, which can be an ADG5413 high-voltage resistant analog switch. When the electrode is selected as a stimulation electrode, a stimulation voltage of up to 20V is directly applied to the electrode, controlling the pre-amplifier analog switch of the signal channel containing that electrode to turn off, preventing signal acquisition in the corresponding signal channel and preventing stimulation voltages of up to tens of volts from directly entering the instrumentation amplifier and damaging the device. When the electrode is used as a acquisition electrode, the pre-amplifier analog switch of the corresponding signal channel remains on, allowing weak physiological signals to pass through.

[0063] Amplifier unit 122 can be an AD8222 instrumentation amplifier, which features low noise, high input impedance, and high common-mode rejection ratio. The instrumentation amplifier receives the differential signal from the preceding analog switch, amplifies it with low noise (e.g., 12.5x), and outputs the amplified physiological signal.

[0064] When the pre-amplifier analog switch unit 121 operates, charge injection generates switching artifacts. These artifacts are much larger than the μV-level physiological signal and are amplified along with the physiological signal, making them unprocessable by subsequent circuits and causing new switching artifacts or signal distortion. To address this issue, this embodiment proposes a circuit structure with a post-amplifier analog switch unit 123 after the amplifier unit 122. The post-amplifier analog switch unit 123 can be a low-voltage analog switch, such as the ADG1634. In this embodiment, the control unit 113 receives the synchronization signal of the stimulation cycle through an isolated communication interface and sends it to the FPGA unit. The FPGA unit then controls the post-amplifier analog switch unit 123 to perform on / off synchronization responses. During the stimulation pulse output, the post-amplifier analog switch is open, cutting off the path of the amplified signal to the subsequent stage, preventing any residual artifacts generated during stimulation from entering the sampling results. During non-stimulation periods, the post-amplifier analog switch is closed, and the amplified physiological signal is transmitted normally to the subsequent amplifier circuit and analog-to-digital converter, thereby realizing the acquisition of the stimulation-induced physiological signal. Understandably, the pre-amplifier analog switch unit 121 only undertakes the task of high voltage protection and operates only on a few channels selected as stimulation electrodes. Although the post-amplifier analog switch unit 123 frequently switches on and off with the stimulation cycle, since it is located after the instrumentation amplifier, the signal entering the post-amplifier analog switch unit 123 has already been amplified by the instrumentation amplifier. The charge injection artifacts generated by the switching action of the post-amplifier analog switch unit 123 are relatively small in amplitude compared with the amplified physiological signal and will not cause signal distortion.

[0065] In this embodiment, the analog switch is positioned after the instrumentation amplifier. The charge injection artifacts generated by its switching action are not further amplified by the instrumentation amplifier, thus significantly reducing their impact on the transmitted physiological signal. This effectively suppresses stimulation artifacts while avoiding signal distortion caused by excessive amplification of pre-amplifier artifacts in traditional solutions, further improving the signal-to-noise ratio and fidelity of the output signal.

[0066] Furthermore, such as Figure 5 As shown, in some embodiments of this application, each signal channel further includes a voltage follower unit 124 and a low-pass filter unit 125, wherein the voltage follower unit 124 is connected between the front-end analog switch unit 121 and the low-pass filter unit 125, and the low-pass filter unit 125 is connected between the voltage follower unit 124 and the amplifier unit 122.

[0067] Specifically, suppressing power frequency interference is a challenge for physiological signal acquisition systems, requiring high input impedance and common-mode rejection ratio (CMRR) at the acquisition front end. To address this, related technologies typically add symmetrical RC low-pass filters to the positive and negative inputs of the instrumentation amplifier to suppress high-frequency radio frequency interference (RFI). However, asymmetry in the parameters of the RC low-pass filter can convert common-mode signals into differential-mode signals, leading to a decrease in the RCM. Simultaneously, the presence of the filter capacitor reduces the input impedance; for example, a 1nF capacitor has an impedance of only about 3.18MΩ for 50Hz power frequency. When used with invasive electrodes, the contact impedance of the electrodes themselves becomes significant relative to this impedance, and the difference in contact impedance between electrodes further disrupts the RC balance, severely degrading the system's common-mode rejection capability in actual clinical environments and resulting in significant power frequency interference. Another related technology attempts to completely remove the RFI filter. In this case, the input impedance is determined by the instrumentation amplifier itself, and the influence of electrode impedance is negligible. However, the bias current of the instrumentation amplifier requires a 10MΩ to 100MΩ bias resistor in parallel between the input and ground, which ironically becomes the upper limit of the input impedance.

[0068] To overcome the aforementioned technical barriers, this embodiment adds a voltage follower unit 124 to the signal channel of the acquisition module. The voltage follower unit 124 can employ an operational amplifier of model OPA2140, which features high input impedance and low bias current. Because the input impedance of the voltage follower is extremely high, typically greater than 10 GΩ, while the contact impedance of the invasive electrodes is typically 1 kΩ to tens of kΩ, it is negligible relative to the input impedance, thus effectively eliminating the adverse effects of contact impedance differences between different electrodes on the common-mode rejection ratio of the subsequent instrumentation amplifier. Simultaneously, the output impedance of the voltage follower is extremely low, enabling it to drive the subsequent low-pass filter unit 125 with low impedance.

[0069] The low-pass filter unit 125 can be composed of a series resistor and a parallel capacitor. It is used to significantly attenuate high frequencies and prevent radio frequency energy from interfering with subsequent circuits. Since the bias current of the voltage follower is extremely low, typically less than 20pA, the leakage current of the preceding analog switching unit 121 can provide a bias circuit, eliminating the need for an additional parallel bias resistor and thus fully preserving the high input impedance characteristics of the voltage follower. Simultaneously, the voltage follower can absorb the bias current of the instrumentation amplifier, eliminating the need for a separate bias resistor for the instrumentation amplifier. Based on this, by ensuring the matching of the positive and negative RC parameters in the low-pass filter unit 125, good common-mode rejection performance can be obtained in clinical scenarios with significant differences in electrode contact impedance, effectively suppressing power frequency interference and stimulation common-mode interference.

[0070] This embodiment utilizes the high input impedance and low bias current characteristics of a voltage follower, providing high input impedance without the need for an additional bias resistor for amplifier unit 122. This overcomes the common-mode rejection ratio (CMRR) degradation caused by the large and significant differences in contact impedance of invasive electrodes, effectively suppressing power frequency interference and stimulating common-mode interference. Simultaneously, a low-pass filter unit 125 is used to filter out high-frequency radio frequency interference. Thus, it ensures high CMRR performance of the analog front-end circuit 10 while avoiding the input impedance limitation imposed by bias resistors in traditional solutions, thereby providing a high-fidelity input signal for subsequent instrumentation amplifiers.

[0071] like Figure 5 As shown, in some embodiments of this application, each signal channel further includes an adjustable high-pass filter unit 126, which is connected between the amplifier unit 122 and the subsequent analog switch unit 123.

[0072] Specifically, the adjustable high-pass filter unit 126 adopts an RC structure, consisting of a resistor and a capacitor connected in series, to isolate the DC polarization voltage generated by the pre-amplifier circuit and prevent the DC component from saturating the subsequent amplifier. Since the frequency of physiological signals is typically below 0.5Hz, the cutoff frequency of the adjustable high-pass filter unit 126 is set to a low value in normal acquisition mode, for example, a cutoff frequency of 0.075Hz, corresponding to a capacitor value of 10uF and a resistor value of 200KΩ, to ensure that low-frequency physiological signals can pass through without loss. However, a lower cutoff frequency means a larger RC time constant τ, causing the signal baseline to take tens of seconds to stabilize when the system is powered on or when the electrodes return to the acquisition state from the stimulation state. To overcome this problem, in this embodiment, the resistor of the high-pass filter unit is designed as an adjustable structure: an analog switch U1 driven by the control unit 113 is connected in parallel on the resistor branch. When rapid baseline recovery is needed, such as after stimulation, the FPGA unit controls the analog switch U1 to turn on, temporarily reducing the resistance value, thereby significantly reducing the RC time constant, and the baseline can stabilize within a few seconds. Once the baseline stabilizes, the FPGA unit disconnects the analog switch U1, and the resistance returns to its original value. At this point, the adjustable high-pass filter unit 126 resumes operation at a low cutoff frequency to ensure that the low-frequency components of subsequent physiological signals are not lost.

[0073] This application embodiment enables the signal baseline to recover and stabilize quickly by setting the time constant of the adjustable high-pass filter unit 126, thereby significantly shortening the signal stabilization time after stimulation, which is beneficial for achieving rapid and reliable continuous acquisition and improving the acquisition efficiency of physiological signals.

[0074] In addition, the aforementioned signal channel also includes a sampling unit 127, which can be an integrated chip of model ADS1299. This chip incorporates a programmable amplifier and a 24-bit analog-to-digital converter (ADC). It is a dedicated chip for EEG acquisition and offers superior performance. The ADS1299 transmits signal data to the FPGA via the SPI interface. The FPGA packages the 32 data channels and transmits them to the system host for storage and display via the LVDS bus.

[0075] In some embodiments of this application, such as Figure 1 As shown, the analog front-end circuit 10 also includes an isolation module 13, which is configured to electrically isolate the stimulation module 11 and the signal acquisition module 12.

[0076] Specifically, as shown in Figure 6(a), without the isolation module 13, the stimulation circuit and the acquisition circuit share a common reference ground (GND). In this case, the system includes multiple signal electrodes (e.g., electrode 1, electrode 2... electrode n), one reference electrode, and one neutral electrode. When electrode 1 and electrode 2 are selected as stimulation electrodes, the stimulation current is expected to be output from the stimulation circuit, passing through electrode 1, human tissue, and electrode 2, and returning to the stimulation circuit, as shown by path I1 in Figure 6(a). However, since the neutral electrode is also connected to the human body and directly to ground, some of the stimulation current will form an unexpected return path from the neutral electrode, as shown by path I2 in Figure 6(a). This shunting results in unequal currents flowing through the two stimulation electrodes. After each cycle of bidirectional stimulation, net charge accumulation occurs on electrode 1 and electrode 2, which may not only cause electrochemical damage to the tissue but also significantly prolong the recovery time of stimulation artifacts.

[0077] As shown in Figure 6(b), in this embodiment, an isolation module 13 is introduced between the stimulation module 11 and the signal acquisition module 12, dividing their grounds into an independent stimulation reference ground GND1 and an acquisition reference ground GND2, with extremely high insulation resistance between them, for example, greater than 1000MΩ. Since there is no DC path between GND1 and GND2, the unexpected current path I2 from the neutral electrode to the stimulation circuit is completely cut off. The stimulation current can only flow in the expected loop formed between electrode 1 and electrode 2, thereby ensuring the charge balance of bipolar stimulation, eliminating the risk of tissue damage, and shortening the artifact recovery time.

[0078] In this embodiment, the isolation module 13 blocks the unexpected path of the stimulation current returning through the neutral electrode and reduces the ground interference between the stimulation circuit and the acquisition circuit, further reducing the coupling energy of the stimulation signal to the acquisition channel, which is beneficial to achieving high-precision physiological signal acquisition.

[0079] Furthermore, in some embodiments of this application, the isolation module 13 includes an isolation communication unit, which is configured to transmit the clock signal of the stimulation cycle to the signal acquisition module 12 in isolation, so that the signal acquisition module 12 switches the on / off state of the signal channel corresponding to the acquisition electrode based on the clock signal in sync with the stimulation cycle.

[0080] Specifically, the isolation communication unit may include an ISO7763DBQR I / O isolation chip and an ISO1540DR I2C interface isolation chip, used to transmit control signals and data between the electrically isolated control unit 113 and the FPGA unit. Because the isolation communication unit has extremely high insulation resistance between its input and output, it can maintain electrical isolation between the stimulation module 11 and the acquisition module while transmitting synchronization signals.

[0081] In this embodiment, the clock signal of the stimulation cycle is transmitted to the signal acquisition module 12 in an electrically isolated manner through an isolated communication unit. This enables the signal acquisition module 12 to accurately synchronize with the on / off state of the stimulation cycle switching signal channel based on the clock signal. Thus, while ensuring electrical isolation between the stimulation module 11 and the signal acquisition module 12 and blocking interference paths, precise timing coordination between the two is achieved, avoiding artifact leakage caused by timing deviations, and further improving the reliability of stimulation synchronization and the quality of the acquired signal.

[0082] In some embodiments of this application, the isolation module 13 further includes an isolation power supply and an isolation capacitor, wherein the isolation power supply is used to provide mutually electrically isolated power to the stimulation module 11 and the signal acquisition module 12, respectively. The isolation capacitor is connected between the electrode and the stimulation module 11, such as... Figure 2 and Figure 4 The isolation capacitors C1 and C2 shown are provided. The isolation capacitors can be 4.7Uf / 50V surface mount capacitors, which are used to block the DC energy in the stimulation signal from being coupled to the signal acquisition module 12.

[0083] Accordingly, please refer to Figure 7 This application also provides a brain-computer interface system, including: The system host 20 includes an integrated neural stimulation and acquisition analog front-end circuit 10 as described in the above embodiment, with the analog front-end circuit 10 connected to the system host 20. The system host 20 may support multiple analog front-end circuits 10.

[0084] The specific configurations and further functional descriptions of the above modules and units are the same as those in the corresponding embodiments described above, and will not be repeated here.

[0085] The brain-computer interface system proposed in this embodiment ensures the safety of the stimulation process and effectively suppresses the common-mode voltage of the stimulation signal relative to the circuit ground, thereby reducing the artifact energy of the stimulation signal coupled to the acquisition channel through the parasitic path. Simultaneously, it effectively avoids signal distortion and artifact interference caused by the coupling of the stimulation signal to the acquisition path, thus ensuring high fidelity of neural signal acquisition under conditions of synchronous stimulation and acquisition.

[0086] For ease of description, the above devices are described separately by function as various units. Of course, in implementing this application, the functions of each unit can be implemented in one or more software and / or hardware.

[0087] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0088] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0089] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

[0090] Although embodiments of this application have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of this application, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. An analog front-end circuit integrating neural stimulation and acquisition, characterized in that, The analog front-end circuit includes multiple electrodes, a stimulation module, and a signal acquisition module. The stimulation module and the signal acquisition module are respectively connected to the multiple electrodes. Any two of the electrodes are selected as stimulation electrodes, and the remaining electrodes are acquisition electrodes. The stimulation module includes a constant current source unit configured to generate a stimulation signal. The stimulation module is configured to control the two stimulation electrodes to be alternately grounded during the stimulation cycle, and to make the ungrounded stimulation electrode output a stimulation signal. The grounding is connected to the negative terminal of the constant current source unit. The signal acquisition module includes multiple signal channels corresponding to each of the electrodes. The signal acquisition module is configured to turn off the signal channel corresponding to the stimulation electrode and synchronously switch the on / off state of the signal channel corresponding to the acquisition electrode during the stimulation cycle, so as to acquire physiological signals in response to the stimulation signal during non-stimulation cycles. Each of the signal channels includes: A pre-amplifier analog switch unit is configured to be turned off when the signal channel corresponds to the stimulation electrode and turned on when the signal channel corresponds to the acquisition electrode, so as to acquire the physiological signal acquired by the acquisition electrode. An amplifier unit is configured to amplify the acquired physiological signal and output the amplified physiological signal. The post-stage analog switching unit is configured to switch on and off synchronously with the stimulation cycle, such that the signal channel corresponding to the acquisition electrode is turned off during the stimulation cycle and turned on during the non-stimulation cycle, so as to transmit the amplified physiological signal to the post-stage circuit during the non-stimulation cycle.

2. The analog front-end circuit according to claim 1, characterized in that, The stimulation module also includes: The H-bridge switching unit includes a first bridge arm and a second bridge arm. The middle node of the first bridge arm is connected to one of the stimulation electrodes, and the middle node of the second bridge arm is connected to the other stimulation electrode. The first ends of the first bridge arm and the second bridge arm are respectively adapted to receive the stimulation signal, and the second ends of the first bridge arm and the second bridge arm are respectively grounded. The first bridge arm and the second bridge arm respectively include a high-side switch and a low-side switch. The H-bridge switching unit is configured to switch the on / off state of the high-side switch and the low-side switch to alternately change the output circuit of the constant current source unit, so that the two stimulation electrodes are alternately grounded during the stimulation cycle. The control unit is configured to control the constant current source unit to generate the stimulation signal and to control the on / off states of the high-side switch and the low-side switch.

3. The analog front-end circuit according to claim 2, characterized in that, The stimulation module further includes a dummy load unit configured to connect to the output circuit of the constant current source unit during the commutation of the stimulation signal in order to suppress commutation glitches in the stimulation signal.

4. The analog front-end circuit according to claim 2, characterized in that, The stimulation module also includes an impedance testing unit and a mode switching unit; The mode switching unit is configured to control the H-bridge switching unit to connect to one of the constant current source unit and the impedance testing unit; The impedance testing unit is configured to measure the impedance between the stimulation electrodes when the H-bridge switch unit is connected to the impedance testing unit, so as to detect whether the stimulation electrodes have abnormal contact based on the measurement results.

5. The analog front-end circuit according to claim 1, characterized in that, Each of the signal channels further includes a voltage follower unit and a low-pass filter unit, wherein the voltage follower unit is connected between the front-end analog switch unit and the low-pass filter unit, and the low-pass filter unit is connected between the voltage follower unit and the amplifier unit.

6. The analog front-end circuit according to claim 1, characterized in that, Each of the signal channels also includes an adjustable high-pass filter unit connected between the amplifier unit and the subsequent analog switch unit.

7. The analog front-end circuit according to claim 1, characterized in that, The analog front-end circuit also includes an isolation module configured to electrically isolate the stimulation module and the signal acquisition module.

8. The analog front-end circuit according to claim 7, characterized in that, The isolation module includes an isolation communication module, which is configured to transmit the clock signal of the stimulation cycle to the signal acquisition module in isolation, so that the signal acquisition module switches the on / off state of the signal channel corresponding to the acquisition electrode in sync with the stimulation cycle based on the clock signal.

9. A brain-computer interface system, characterized in that, The brain-computer system includes: System host; And the analog front-end circuit for integrated neural stimulation and acquisition as described in any one of claims 1 to 8, wherein the analog front-end circuit is connected to the system host.

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